Method of producing concentrated phosphoric acid

ABSTRACT

Monocalcium phosphate, advantageously in the form of single superphosphate or triple superphosphate, is mixed with sulfuric acid or ammonium bisulfate and methanol. The monocalcium phosphate and the sulfuric acid or ammonium bisulfate react to form phosphoric acid and a precipitate which contains calcium sulfate. The phosphoric acid is substantially entirely dissolved in the methanol. Next the methanol containing the dissolved phosphoric acid is separated from the solid precipitate by decantation, filtration or centrifugation. By evaporation of the methanol a phosphoric acid concentrate is obtained, or by the addition of a base to the methanolic acid solution, the corresponding phosphate salts are formed and precipitated in an easily separatable and dryable form.

United States Patent Rubin et al.

[ 51 May 16,1972

[54] METHOD OF PRODUCING CONCENTRATED PHOSPHORIC ACID [72] Inventors:Allen G. Rubin, Walnut Creek; Nicholas Kalmar, Berkeley, both of Calif.

[73] Assignee: B. D. Bohna 8: Company, Inc., San Francisco, Calif.

[22] Filed: July 3, 1969 [21] Appl. No.: 838,964

[51] Int. ......C01b 15/18, C0lb 25/28, C0lb 25/22, COlb 25/30 [58]Field olSearch ..23/l65, 165 C, 107; 71/43 [56] References Cited UNITEDSTATES PATENTS Niekerson et a1 ..23/1 65 Moldovan et a1 ..23/ 107ABSTRACT Monocalcium phosphate, advantageously in the form of singlesuperphosphate or triple superphosphate, is mixed with sull'uric acid orammonium bisulfate and methanol. The monocalcium phosphate and thesulfuric acid or ammonium bisulfate react to form phosphoric acid and aprecipitate which contains calcium sulfate. The phosphoric acid issubstantially entirely dissolved in the methanol. Next the methanolcontaining the dissolved phosphoric acid is separated from the solidprecipitate by decantation, filtration or centrifugation. By evaporationof the methanol a phosphoric acid concentrate is obtained, or by theaddition of a base to the methanolic acid solution, the correspondingphosphate salts are formed and precipitated in an easily separatable anddryable form.

7 Claims, 1 Drawing Figure METHOD OF PRODUCING CONCENTRATED PHOSPI'IORICACID BACKGROUND OF THE INVENTION Monocalcium phosphate has been producedfor many years in the form of single superphosphate or triplesuperphosphate by the acidulation of phosphate rock. Many plants usesulfuric acid as the acidulating agent to produce single superphosphate.The single superphosphate is usually blended with other materials andused as a fertilizer because of its available phosphate. However, theI50, content of single superphosphate is low, generally in the order of20 to 22 percent, and therefore the value of the single superphosphateproduct is limited. The reaction of sulfuric acid with phosphate rock toproduce monocalcium phosphate in the form of single superphosphate maybe expressed as follows: CaF, 9Ca0 3 P 0, 7l-l,SO, 3Ca(H,PO,), 7CaS0,

Monocalcium phosphate is manufactured as triple superphosphate byreacting phosphate rock with phosphoric acid. This reaction is generallyconducted by phosphoric acid producers who use impure phosphoric acidfor acidulating phosphate rock. A substantial part of this impurephosphoric acid is sludge acid which is a byproduct left over from theclarification of the phosphoric acid prepared for commercial sale. Thetriple superphosphate contains approximately 46 percent available P,OHowever, the triple superphosphate is still a low value product comparedto superphosphoric acid having a high P content. The reaction betweenphosphate rock and phosphoric acid to produce monocalcium phosphate inthe form of triple superphosphate may be set forth as follows:

SUMMARY OF THE INVENTION In accordance with the present invention,concentrated phosphoric acid of high purity is obtained from monocalciumphosphate present in single superphosphate or triple superphosphate bymixing monocalcium phosphate with methanol and an acidic sulfateselected from the group con sisting of sulfuric acid and ammoniumbisulfnte. For each part (weight) of the monocalcium phosphate used inthe process from about 0.8 to 10 parts, preferably 1 to 3 parts, ofmethanol are employed. For each mol of the monocalcium phosphate in theprocess feed an amount of the acid in the range from about 0.5 to 2.0,preferably 0.9 to 1.2, times the metathetical requirement is used. Theperiod of slurrying (mixing) the process feed is not particularlycritical. Depending upon the intensity of agitation and the particlesize of the monocalcium phosphate the period of mixing is from about 1minute to l0 hours. During mixing the temperature of the mixture ismaintained at or below the boiling point of the methanol.

The solid and liquid fractions of the resulting slurry are thenseparated by a suitable mechanical means such as filtration,centrifugation or decantation, preferably by eentrifugation. The solidfraction of the slurry is mainly calcium sulfate and impurities whichare insoluble in methanol. The liquid fraction is a useful methanolicsolution of phosphoric acid which may be conveniently concentrated tophosphoric acid by evaporation of the methanol or converted to usefulphosphate salts by neutralization with a suitable inorganic base. In thelatter case, the salts produced precipitate from the methanolic solutionand may be conveniently recovered by filtration.

Surprisingly, the formation of calcium sulfate as a precipitate at theliquid-solid phase interface of the slurry does not interfere with thesubstantially total (90 percent plus) conversion of the water solublephosphorous values in the feed to phosphoric acid. Water in anyappreciable amount is neither necessary nor desirable for the practiceof the instant process. Water which may be present in the monocalciumsalt feed or acid is extracted by the methanol and in the main remainswith the phosphoric acid when the methanol is evaporated. Thus water, ifpresent, in the process feed lowers the P,0, value (weight percent) ofthe recovered phosphoric acid or must be removed by heating the acid atan elevated temperature (100 300 C-).

The presence of a substantial amount of water in the present slurrysystem is undesirable where relatively high purity product is desiredbecause in this event the water tends to increase the solubility ofimpurities, salts and the like, in the methanolic solution. These, ofcourse, end up in the phosphoric acid concentrate. A substantial amountof water based upon methanol, is in general an amount above about 15parts (weight) per 100 parts of methanol.

On the other hand, the complete miscibility of water with methanol isadvantageous where relatively wet monocalcium phosphate salt feed mustbe used or where only relatively dilute (60-75 percent) acid isavailable for the acidification. So long as the water content of theslurry relative to methanol does not exceed 50-60 parts per 100 parts ofmethanol, a useful extraction of phosphoric acid can be achieved in asingle liquid phase system, although as noted above, the removal of thewater and impurities from the phosphoric acid concentrate adds to theprocess burden. Preferably the amount of water present in the slurry isless than 5 parts per 100 parts of methanol.

Therefore, in the instant process the use of methanol, which is anexcellent solvent for both water and phosphoric acid, provides a singleliquid phase system which reduces the handling problems in the process,minimizes solvent losses, allows flexibility in the choice of the acidreactant, and permits the phosphoric acid compound to be separateddirectly from the solvent.

The process of the present invention provides unique advantagesincluding: (l) the production and extraction of phosphoric acid frommonocalcium phosphate in a single reaction stage; (2) an efficientsimple reaction system usually capable of yields of over 90 percent ofthe water soluble R0 content of the superphosphate starting feed; and ingeneral of yields of over percent of the total [50,; (3) the use of aprocess medium having a high solvent selectivity effect in that methanolsolubilizes phosphoric acid and at the same time rejects (as a solvent),impurities normally associated with fertilizer grade monocalciumphosphates; (4) the use of a solvent fully miscible with water obviatingmultiple liquid phase formations and phase separations as well as solutedistribution problems between several liquid phases; (5) the use of asolvent having a relatively low boiling point and low latent heat ofvaporization, thereby greatly reducing the process burden normallyexperienced; (6) the use of a liquid medium permitting direct recoveryof the phosphoric acid concentrate from the solvent; (7) the use of asolvent which requires no cosolvent for effective practice of theinvention.

By the metathetical requirement as used herein is meant the number ofequivalents, acid-base, of the sulfate acid required to liberatephosphoric acid from 1 mol of the monocalcium phosphate feed. Thetheoretical value is 2 equivalents of acid per mol of the salt. However,where the monocalcium phosphate salt feed is somewhat impure andcontains inert matter, or where a relatively higher purity phosphoricacid concentrate is desired, only about 1.8 equivalents of the acidshould be used per mol of the salt. Where, on the other hand, it isdesired to maximize phosphoric acid recovery or where a minor portion ofthe sulfate acid is lost to acid consuming side reactions, about 2.4equivalents of the sulfate acid per mol of the monocalcium phosphatesalt feed should be employed. in terms of the metathetical requirementthe preferred range of acid is 0.9 L2 times the metathetical value;broadly the range 0.5 2.0 is satisfactory. Sulfuric acid, of course,contains two equivalents of acid per mol whereas ammonium bisulfatecontains but one equivalent per mol.

Monocalcium phosphate in general may be used as a process feed herein.Several forms are known and, of these, particularly desirable as feedsare the so-called single superphosphate and triple superphosphate ofcommerce.

The temperature used in the slurry reaction system of the process of theinvention is desirably in the range below the boiling point of themethanol solvent and above about C., preferably in the range from about15 to 50 C. Higher temperatures may be used but such use is lesseconomical because pressure equipment would then be necessary in orderto maintain the methanol in the liquid phase. The use of lowertemperatures on the other hand is increasingly unsatisfactory because ofincreasing viscosity effects and the like as the temperature is reduced.

The size of the monocalcium phosphate solids fed to the reactor may varywidely. Large pieces, as much as 2 inches in diameter and larger, may beemployed satisfactorily, although for efficient recovery of thephosphoric acid content, residence times in the slurry reactor must belonger and agitation must be more intense where the feed has arelatively large size. Preferably, the monocalcium phosphate feed has aparticle size on the order of granular range and smaller, below about anaverage diameter of approximately one-eighth of an inch. 1n the lattercase, the phosphoric acid liberating reaction and the dissolution of thephosphoric acid in the methanol appears to occur almost immediately uponthe mixing of the feed streams. Broadly satisfactory mixing or slurryingtimes are in the range from about 1 minute to 10 hours or more.

The monocalcium phosphate powder or granular material and the ammoniumbisulfate or sulfuric acid are mixed together in a methanol solvent.Sufficient methanol is used to provide a stirrable slurry. If too muchmethanol is employed, the expense of the process is increased becausethe methanol must later be separated by evaporation or other means fromthe phosphoric acid compound product. For practical purposes it has beenfound that about one part of methanol to one part of solids provides asatisfactory reaction mixture.

Either sulfuric acid, ammonium bisulfate or mixtures thereof may beemployed to acidify the monocalcium phosphate and prodrlce phosphoricacid. The reaction with sulfuric acid may be set forth as follows:

Ca( H30 H 80 CaSO, 2 I l PO, and the reaction of ammonium bisulfate isas follows:

Ca(H,PO,, 2 NI'LHSO CaSO, (NH,),SO., +2H PO, These acids may becharacterized as sulfate acids selected from the group consisting ofsulfuric acid and ammonium bisulfate. Both sulfuric acid and ammoniumbisulfate react with the monocalcium phosphate substantially completelyin the methanol solution.

The calcium from the monocalcium phosphate is precipitated as hydratedcalcium sulfate or gypsum along with other impurities present in thestarting material. In addition when ammonium bisulfate is used as thestarting acid, ammonium sulfate is also precipitated.

A preferred embodiment of the process of the present invention isillustrated in the Figure. lnto stirred tank reactor 1, granulated orpowdered monocalcium phosphate via line 2, 93 percent sulfuric acid vialine 3 and methanol (fresh make-up methanol via line 4 plus recyclemethanol via line 5) via line 6 are charged in the relative proportionsof 1-3 parts (weight) of methanol per part of the monocalcium phosphatesalt and 1 mol of the sulfuric acid per mol of the salt, and theresulting slurry is stirred while maintaining the temperature of themixture in the range 25-40 C. After a residence time of 0.5 1 hour, theresulting reaction mixture is withdrawn from reactor 1 via line 7 anddelivered to separator 8 (a centrifuge) wherein the solid fraction ofthe slurry is separated from the liquid fraction and is washed withadded methanol via line 9, withdrawn from separator 8 via line 10 anddelivered to dryer 11. The separated liquid fraction which is amethanolic solution of phosphoric acid extract plus a small quantity ofthe above noted methanol wash solution is withdrawn from separator 8 vialine 14 and delivered to the distillation column 15 where methanol isfractionated from the phosphoric acid. Methanol vapor from distillationcolumn 15 via line 17 and from dryer ll via line 12 is delivered tocondenser 18 and the recovered methanol is recycled to the process vialine 5. The

phosphoric acid concentrate from distillation column 15 is delivered toproduct storage via line 16 or for further processing as desired.

The phosphoric acid concentrates produced in accordance with thisinvention have a high P 0, content, generally of the order of 50 to 60percent by weight. By application of heat the concentrate may easily andeconomically be further concentrated to superphosphoric acid (a mixtureof orthophosphoric and polyphosphoric acids) having about a 72 percent[50, content. Transportation costs per unit of F50, are, of course,substantially reduced.

As an alternative, phosphoric acid compounds may be precipitated fromthe methanol solution as salts. Neutralization of the phosphoric acidwith ammonia results in the formation of a very pure ammonium phosphateprecipitate having a high I50, value. This precipitate may be readilyrecovered by filtration and is a water soluble, valuable fertilizer.When a calcium compound is precipitated, a useful animal feed isproduced. When sodium hydroxide is used to neutralize the methanolicphosphoric acid solution, sodium phosphate which is useful as adetergent additive is precipitated. Similarly, the use of potassiumhydroxide for the neutralization yields potassium phosphate which isalso a useful fertilizer.

The following examples further illustrate the practice of the invention.All references to amounts as parts are in parts by weight.

EXAMPLE I Commercial run-of-pile triple superphosphate was employed inthis example and had the following analysis:

Total 1H0, 47.20% Water-soluble H0, 41 18% 50 3.87% Ca 14.20%

30.0 parts of triple superphosphate were charged into a tank providedwith an agitator. Next 43.0 pans of methanol and 21.2 parts of ammoniumbisulfate were added to the tank. The resulting slurry was stirred for 4hours 50 minutes after which the slurry was filtered on a plate andframe filter press. The filtration residue was washed with freshmethanol to displace any remaining P 0 laden solvent, and the washingswere combined with the main filtrate. 63.9 parts of filtrate wereobtained which contained a total of 12.31 parts of P 0 0.42 parts NH,and 2.18 parts of S0,. The washed filtration residue was dried to removeadhered methanol. Upon analysis the dried residue was found to contain1.85 parts of P 0 4.26 parts of Ca, 2.90 parts NH, and [6.68 parts ofS0,. The combined filtrate and washings were evaporated to recover themethanol and yielded a concentrated acid having the following weightanalysis:

P 1 5 59.03% 50 10.46% NH, 2.0m F 44 ppm CBO 15 ppm 2"3' 38 a Fi MgO 380ppm Based on the water-soluble P 0, in the in the starting material, therecovery yield as phosphoric acid was 98.2 percent.

EXAMPLE ll Commercial granular single (normal) superphosphate was groundto pass a 20 mesh screen. The ground material had the followinganalysis:

Total 150, 22.46% Water-soluble P,O, 17.45% 50, 35.12% Ca 21.63%

50.0 parts of this ground single superphosphate were put into alaboratory blender. 50.0 parts of methanol and 22.9 parts of ammoniumbisulfate were added and the resulting mixture was blended for 5minutes. The blended slurry was immediately filtered and yielded 63.8parts of filtrate which contained a total of 8.31 parts of P,O,, 0.36parts NH, and 2.27 parts of S0,. The residue from the filtration waswashed with fresh methanol to remove any remaining methanol solubleP,O,, and the washings were combined with the main filtrate. The washedresidue was dried and upon analysis was found to contain 2.92 parts of150,, 10.82 parts of Ca, 3.22 parts NH. and 34.40 parts of S0,. Thecombined filtrate and washings were evaporated to recover the methanoland yielded a concentrated acid with the following weight analysis:

P O, TN 60.13%

50, 16.42% NH, 2.59% F l 13 ppm CaO 25 ppm ALO, 80 ppm Fe,0, 100 ppm MgO350 ppm 95.2 percent of the water-soluble P 0, in the starting materialwas recovered as concentrated phosphoric acid.

EXAMPLE II] 30.0 parts of commercial run-of-pile triple superphosphate(the same material as in Example 1) were put into an agitated vessel.30.0 parts of methanol and 9.0 parts of 93 percent sulfuric acid wereadded to the vessel. The resulting slurry was stirred for 3 hours 30minutes after which it was settled and the clear liquid was decanted.The settled solids were washed with methanol to displace any solventcontaining P and the washings were combined with the main decantedliquor. 50.9 parts of rich solvent were obtained which contained a totalof 12.44 parts of H0 and 1.58 parts of S0,. The washed solids were driedand, when analyzed, were found to contain 1.72 parts of P 0 4.26 partsof Ca and 7.78 parts of S0,. The rich solvent was evaporated to recoverthe methanol and yielded a concentrated acid with the following weightanalysis:

P 0, 59.54% S0, 7.57% F 978 ppm CaO ppm Al,0, I50 ppm Fe,0, 2500 ppm MgO500 ppm Of the water-soluble 1 ,0 in the starting material, 99.3 percentwas recovered as concentrated phosphoric acid.

EXAMPLE IV 50.0 parts of commercial granular single superphosphate (thesame material as in Example ll) was thoroughly mixed with 50.0 parts ofmethanol and 10.5 parts of 96 percent sulfuric acid in a high speedblender for 5 minutes. The blended mixture was separated into a liquidportion and a solid portion. The solids were washed with fresh methanolto insure removal of all P,O,-containing solvent, and the washings werecombined with the liquid portion. 65.9 parts of liquid were obtainedwhich contained a total of 9.36 parts of P 0, and 2.14 parts of S0,. Thedried solids were found to contain 1.87 parts of P,O,, 10.82 parts of Caand 25.29 parts of S0 The liquid was evaporated to recover the methanoland produced a concentrated acid with the following weight analysis:

P,O,, 58.84% S0, 13.43% F 690 ppm C a0 ppm A1,0 1000 ppm Fe,O, 3000 ppmMgO 1800 ppm In this example, 107.2 percent of the water-soluble R0, inthe starting material was recovered as concentrated phosphoric acid.This indicates that a portion of the non-water soluble P 0, wasconverted to a soluble form as a result of the treatment.

What is claimed is:

1. The method of producing concentrated phosphoric acid which comprisesreacting monocalcium phosphate with a sulfate acid by mixing thereactants and methanol while maintaining the temperature of the mixturein the range below the boiling point of methanol and above about 0 C.for a period in the range from about 1 minute to 10 hours, wherein foreach mol of the phosphate salt the amount of acid is in the range of 0.5to 2.0 times the metathetical requirement. and wherein said acid isselected from the group consisting of sulfuric acid, ammonium bisulfateand mixtures thereof; physically separating the resulting reactionmixture into a liquid fraction of phosphoric acid dissolved in methanoland a solid fraction; and then separating phosphoric acid from saidliquid fraction by evaporating said methanol; the liquid present in saidreaction mixture constituting substantially the total amount of liquidemployed in said method of producing concentrated phosphoric acid.

2. The method of claim 1 wherein for each part by weight of the salt,there is present an amount of methanol in the range 0.8 to 10 parts, andthe mixture contains in parts by weight less than 50-60 parts of waterper parts of methanol.

3. The method of claim 1 wherein the amount of acid is in the range fromabout 0.9 to 1.2 times the metathetical require ment; in that the amountof methanol is in the range from about 1 to 3 parts; in that thetemperature is in the range from about 15 to 50 C.; in that the salt hasan average diameter of less than about Au-inch; and in that in parts byweight less than about 5 parts of water per 100 parts of methanol arepresent in the mixture.

4. A method for the production of concentrated phosphoric acid whichcomprises reacting monocalcium phosphate with a sulfate acid by mixingthe reactants and methanol while maintaining the temperature of themixture in the range from about 15 to 50 C. for a period in the rangefrom about 1 minute to 10 hours, wherein for each mol of the phosphatesalt the amount of acid is in the range from about 1.8 to 2.4equivalents, wherein for each part by weight of the salt, there ispresent an amount of methanol in the range from about 0.8 to 3 parts,wherein said acid is selected from the group consisting of sulfuricacid, ammonium bisulfate and mixtures thereof, and wherein said mixturecontains in parts by weight less than about 5 parts by weight of waterper 100 pans of methanol; physically separating the resulting reactionmixture into a liquid fraction and a solid fraction; and removingmethanol from the liquid fraction by fractional distillation; the liquidpresent in said reaction mixture constituting substantially the totalamount of liquid employed in said method of producing concentratedphosphoric acid.

5. The method of claim 4 further characterized in that the methanoldepleted liquid fraction is heated at a temperature in the range fromabout 100 to 300 C., thereby further concentrating the methanol depletedfraction and producing a phosphoric acid having a P 0, content of atleast about 72 weight percent.

6. The method of producing an inorganic phosphate salt which comprisesreacting monocalcium phosphate with a sulfate acid by mixing thereactants and methanol while maintaining the temperature of the mixturein the range below the boiling point of methanol and above about 0 C.for a period in the range from about 1 minute to 10 hours, wherein foreach mol of the phosphate salt the amount of acid is in the range of 0.5to 2.0 times the metathetical requirement, and wherein said acid isselected from the group consisting of sulfuric acid, ammonium bisulfateand mixtures thereof; physically separating the resulting reactionmixture into a liquid fraction of phosphoric acid dissolved in methanoland a solid fraction; and then precipitating an inorganic phosphate saltselected from the group consisting of ammonium phosphate, alkali metalphosphates and alkaline earth metal phosphates from the liquid fractionof phosphoric acid dissolved in methanol by adding a base having acorresponding cation to said liquid fraction; the liquid present in saidreaction mixture and said base constituting substantially the totalamount of liquid employed in said method of producing an inorganicphosphate salt.

7. The method of producing an inorganic phosphate salt which comprisesreacting monocalcium phosphate with a sulfate acid by mixing thereactants and methanol while maintaining the temperature of the mixturein the range from about to 50 C. for a period in the range from about 1minute to 10 hours, wherein for each mol of the phosphate salt theamount of acid is in the range from about 1.8 to 2.4 equivalents,wherein for each part by weight of the salt, there is present an amountof methanol in the range from about 0.8

to 3 parts, wherein said acid is selected from the group consisting ofsulfuric acid, ammonium bisulfate and mixtures thereof, and wherein saidmixture contains in parts by weight less than about 5 parts by weight ofwater per parts of methanol; physically separating the resultingreaction mixture into a liquid fraction and a solid fraction; and thenprecipitating an inorganic phosphate salt selected from the groupconsisting of ammonium phosphate, alkali metal phosphates and alkalineearth metal phosphates from the liquid fraction of phosphoric aciddissolved in methanol by adding a base having a corresponding cation tosaid liquid fraction, the liquid present in said reaction mixture andsaid base constituting substantially the total amount of liquid employedin said method of producing an inorganic phosphate salt.

l i t

2. The method of claim 1 wherein for each part by weight of the salt,there is present an amount of methanol in the range 0.8 to 10 parts, andthe mixture contains in parts by weight less than 50- 60 parts of waterper 100 parts of metHanol.
 3. The method of claim 1 wherein the amountof acid is in the range from about 0.9 to 1.2 times the metatheticalrequirement; in that the amount of methanol is in the range from about 1to 3 parts; in that the temperature is in the range from about 15* to50* C.; in that the salt has an average diameter of less than about 1/8-inch; and in that in parts by weight less than about 5 parts of waterper 100 parts of methanol are present in the mixture.
 4. A method forthe production of concentrated phosphoric acid which comprises reactingmonocalcium phosphate with a sulfate acid by mixing the reactants andmethanol while maintaining the temperature of the mixture in the rangefrom about 15* to 50* C. for a period in the range from about 1 minuteto 10 hours, wherein for each mol of the phosphate salt the amount ofacid is in the range from about 1.8 to 2.4 equivalents, wherein for eachpart by weight of the salt, there is present an amount of methanol inthe range from about 0.8 to 3 parts, wherein said acid is selected fromthe group consisting of sulfuric acid, ammonium bisulfate and mixturesthereof, and wherein said mixture contains in parts by weight less thanabout 5 parts by weight of water per 100 parts of methanol; physicallyseparating the resulting reaction mixture into a liquid fraction and asolid fraction; and removing methanol from the liquid fraction byfractional distillation; the liquid present in said reaction mixtureconstituting substantially the total amount of liquid employed in saidmethod of producing concentrated phosphoric acid.
 5. The method of claim4 further characterized in that the methanol depleted liquid fraction isheated at a temperature in the range from about 100* to 300* C., therebyfurther concentrating the methanol depleted fraction and producing aphosphoric acid having a P2O5 content of at least about 72 weightpercent.
 6. The method of producing an inorganic phosphate salt whichcomprises reacting monocalcium phosphate with a sulfate acid by mixingthe reactants and methanol while maintaining the temperature of themixture in the range below the boiling point of methanol and above about0* C. for a period in the range from about 1 minute to 10 hours, whereinfor each mol of the phosphate salt the amount of acid is in the range of0.5 to 2.0 times the metathetical requirement, and wherein said acid isselected from the group consisting of sulfuric acid, ammonium bisulfateand mixtures thereof; physically separating the resulting reactionmixture into a liquid fraction of phosphoric acid dissolved in methanoland a solid fraction; and then precipitating an inorganic phosphate saltselected from the group consisting of ammonium phosphate, alkali metalphosphates and alkaline earth metal phosphates from the liquid fractionof phosphoric acid dissolved in methanol by adding a base having acorresponding cation to said liquid fraction; the liquid present in saidreaction mixture and said base constituting substantially the totalamount of liquid employed in said method of producing an inorganicphosphate salt.
 7. The method of producing an inorganic phosphate saltwhich comprises reacting monocalcium phosphate with a sulfate acid bymixing the reactants and methanol while maintaining the temperature ofthe mixture in the range from about 15* to 50* C. for a period in therange from about 1 minute to 10 hours, wherein for each mol of thephosphate salt the amount of acid is in the range from about 1.8 to 2.4equivalents, wherein for each part by weight of the salt, there ispresent an amount of methanol in the range from about 0.8 to 3 parts,wherein said acid is selected from the group consisting of sulfuricacid, ammonium bisulfate and mixtures thereof, and Wherein said mixturecontains in parts by weight less than about 5 parts by weight of waterper 100 parts of methanol; physically separating the resulting reactionmixture into a liquid fraction and a solid fraction; and thenprecipitating an inorganic phosphate salt selected from the groupconsisting of ammonium phosphate, alkali metal phosphates and alkalineearth metal phosphates from the liquid fraction of phosphoric aciddissolved in methanol by adding a base having a corresponding cation tosaid liquid fraction; the liquid present in said reaction mixture andsaid base constituting substantially the total amount of liquid employedin said method of producing an inorganic phosphate salt.